An increasing number of wireless communication standards as applied to a portable device and a trend towards ever smaller, slimmer and lighter portable devices may cause major design challenges for antennas or radiators (hereinafter referred to as radiator in this document). Radiators represent a category of components that may fundamentally differ from other components in the portable device. For example, the radiator may be configured to efficiently radiate in free space, whereas the other components are more or less isolated from their surroundings.
Electrically small radiators are typically of resonant type. In other words, a length of a metallic radiator element is bound to a fraction of a wavelength at an operating frequency. In terms of impedance bandwidth (BW) and radiation efficiency, radiator miniaturization is a size versus performance trade-off.
A challenge of covering a single wide frequency band or multiple frequency bands may be solved with use of multiple radiators. Such a solution may not practical, because more radiator space and interconnections are needed in the portable device. Furthermore, mutual coupling between individual radiators may cause severe operating problems.
Many current portable device radiators are of wide-band or of multiple band type. In many of these radiators, the multiple band operation is achieved at the expense of a larger radiator size, and thereby necessitating performance compromises between the individual bands.